When the viewfinder program gives you the error that the disk is full, the program is referring to the cameras proprietary hard drive. When the camera has reached a limit of 255 scans its scan log has to be erased and all the camera files with it. again I repeat the hard drive in question is the cameras hard drive not the computer hard drive.

to access the cameras hard drive you must:

Be currently in the viewfinder program and navigate to File>File manager...

Once the file manager window is open select all the files by pressing hot key combo "command+A" (command is the key with the clover shape on it)

Now click the delete button on the file manager window and wait for the files to be erased.